Full suspension, PTO air compressor, 1 medium motor for steering, 2 XL motors for driving.
About this creation
The back axles are suspended by a 3-link system and the frame rests on them via a beam on each side that is connected to the frame, but not the axles, works great! Easy to build, try it, the pictures explain it better.
The black hose is simply used to store air with the blue tank
The front axle is a pivot/swing style.
The transmission uses no 8 tooth gears and no bevel/crown gears for maximum strength. I had to "gear-up" the transmission because it was way too slow, and it's still really slow, but pulls well. The drive shaft on the back goes to the axles. Transmission can either power the wheels or the air compressor by simply flipping the switch. The motor mounting was inspired by Sariel's Mammoet Kenworth and uses the yellow knob gears for durability.
It sure looks big and I am astonished by the fact that the engines can carry and steer this humongous truck! I can't believe it, but it's true, Haha! Wel now I'm going to build a Lego sportscar driven by two engines too.